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From Wikipedia, the free encyclopedia

A diagram of the linemen, with defensive linemen (in 4-3 formation)
in red and offensive linemen in green.

In American football, a
lineman is a player who specializes in play at the
line of
scrimmage. The linemen of the team currently in possession of
the ball are the offensive line, while linemen on
the opposing team are the defensive line. A number
of NFL rules specifically address restrictions and requirements for
the offensive line. The defensive line is covered by the same rules
that apply to all defensive players. Linemen are usually the
largest players on the field in both height and weight, since their
positions usually require less running and more strength than other
positions.

Offensive
line

The interior offensive line consists of the center, who is responsible
for putting the ball into play, two guards who flank the center,
and two offensive tackles who flank the
guards; NFL rules require that a team have all five of these
interior linemen on the field for every offensive play. In addition
to the interior line, a full offensive line may also include a tight end outside one or
both of the tackles.

Interior offensive linemen are not eligible to catch forward
passes, and are not allowed to have advanced past the line of
scrimmage at the time a pass is thrown unless they are in contact
with a defensive player. Tight ends, however, are eligible to catch
passes.

On running plays, the primary job of the offensive line is to
create space for the ball carrier to run, either by pushing all
defensive players backwards past the line of scrimmage, or by
pushing defensive players to the side to allow the ball carrier to
run past them. On some running plays, an offensive lineman will
pull by backing out of his initial position and
running behind the other offensive linemen to engage a defensive
player beyond the initial width of the offensive line; in modern
games this duty usually falls to guards.

On passing plays the offensive line is responsible for stopping
defensive players from tackling the quarterback before he has
thrown the ball. Stopping these players indefinitely is usually not
possible, so the main objective of the offensive line is to slow
them down, providing the quarterback with several seconds to
identify an open receiver and throw the ball.

An offensive lineman's motion during a play is often limited to
just a few quick steps to establish position, followed by a
wrestling match similar to sumo.
Offensive linemen thus tend to be the largest players on the field,
with excellent agility and balance but limited straight-line
running speed.

Defensive
line

The defensive line consists of one or two defensive tackles and two defensive ends who play outside the
defensive tackles. The defensive line works with the linebackers to try to control the line of
scrimmage. The 4-3 defensive formation most commonly used in the
NFL employs two defensive tackles (and a defensive line of four
men, with three linebackers behind them), while the 3-4 formation
uses just a single defensive tackle, called the nose tackle (and a
defensive line of three men, with four linebackers behind
them).

On running plays, the goal is to tackle the ball carrier. The
defensive line attempts to maintain their original formation (even
spacing without holes), but also to prevent any members of the
opposing offensive line from successfully engaging the linebackers,
who chase down the ball carrier. The defensive tackles are usually
the most skilled run defenders on the team.

On passing plays, the defensive line tries to reach the
quarterback. Ideally, the defensive players are able to tackle the
quarterback for a loss (a sack), but in practice
the quarterback will usually manage to throw the ball before an
actual tackle is made; the goal is thus to put pressure on the
quarterback as quickly as possible to force him to throw the ball
before he can find an open receiver. Defensive ends are usually the
most skilled pass rushers on the team. In order to increase the
pressure on the quarterback, teams will often have players other
than the defensive line attempt to tackle the quarterback; this is
called a blitz.

Because the defense does not know whether the offense is
attempting to run a passing play or a running play (or whether a
quarterback will give up on an attempt to pass and instead run with
the ball), they must balance passing and running strategies:
running around offensive linemen and avoiding contact may allow
faster pressure on a quarterback, but it also leaves a hole in the
defensive line and frees an offensive lineman to engage a
linebacker, enabling a big running play.

Defensive linemen---particularly defensive ends--are called upon
to do more running than offensive linemen, thus they usually tend
to be somewhat smaller and faster.